Date of Award


Degree Name

Master of Science


Molecular Biology Microbiology and Biochemistry

First Advisor

Watabe, Kounosuke


AN ABSTRACT OF THE THESIS OF Leon McWilliams, for the Masters of Science Degree in Medical Microbiology and Immunology, presented March 5, 2009 at Southern Illinois University. IN VITRO ANTIMICROBIAL SUSCEPTIBILITY OF S. AUREUS IN SUSPENSIONS, BIOFILMS, AND RESUSPENDED BIOFILMS MAJOR PROFESSOR: Dr. Kounosuke Watabe Whether in nature, a laboratory, or in a hospital, microorganisms exist by attaching themselves to living and nonliving objects. The range of objects microorganisms can adhere to vary from soil, internal medical devices, living tissues such tooth enamel and the lungs (1-4). As these microorganisms grow on the various objects, they develop polysaccharide layers (slime) that aid in attachment and development of a matrix (1). The development of the microorganism colony, and subsequent slime layer, is called a biofilm. The study of biofilms is of such clinical significance because of the microorganisms' altered physiological state in the biofilm. Previous studies have reported that microorganisms have significantly higher resistance in biofilm form as opposed to floating cells (1-2,5). Theories for this phenomenon include slower growth rates of cells, enzymes deactivating the antimicrobials before they can completely diffuse through the biofilm, and the very sub-population of cells that form a biofilm form a highly protected phenotypic state (1,2,3). Researchers continue to debate whether this altered physiological state of microorganisms in biofilms is due to intrinsic or extrinsic factors. The increased resistance to antimicrobials makes biofilms a very significance and expensive problem in the medical field. According to the Center for Disease Control (CDC), the medical community spends over 6 billion dollars in its battle against antibiotic-resistant microorganisms (3,38). Many indwelling medical devices such as catheters and pacemakers are susceptible to development of biofilms. Once a biofilm has been established on an indwelling medical device, clumps of cells periodically break off from the biofilm. These clumps of cells can travel in the blood stream, causing reoccurring systemic infections in the host. Due to biofilms' extraordinary resistance to antimicrobials and the occasional breakage of clumps from the primary structure, an individual infected by a biofilm may have to fight off its ill effects for months, years, even the rest of his or her life ( 3). In our research, we will study of Staphylococcus aureus. This microorganism is recognized as a key pathogen in human diseases. S. aureus is a frequent cause of community-acquired infections such as endocarditis, osteomyelitis, pneumonia, and septic arthritis (2,4). According to the CDC, the medical community invests 160 million dollars annually to combat emerging antibiotic-resistant strains of S. aureus (34). S. aureus's wide spectrum of diseases is due to its great ability to adhere to many inert and biological surfaces (4). For our project, we will use the antimicrobials vancomycin, oxacillin, and synercid. We will study the antimicrobial susceptibility of S. aureus by using suspensions, biofilms, and resuspended biofilms.




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